Means for drawing, forming, shaping, or embossing sheet metal and the like



uuu| uu w I "W 7 I FIDPOOQ OP 2,399,775 W y 1946. v. WHISTLER ETAL 2,399,775

MEANS FOR DRAWING, FORMING, SHAPING, OR Q EMBOSSING SHEE ETAL AND THE LIKE J Filed 11.7, 1943 2 Sheets-Sheet l II I Ian heme VWZwfZer W d azyralf e n.

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May 7, 1946.

L. V. HISTLER ET AL MEANS FOR DRA 2 Sheets-Sheet 2 J. [ll/4 Ml/iii, 51 W a 45 2 $2 io( 41) 4 V, ai-

UNITED STATES PATENT OFFICE MEANS FOR DRAWING, FORMING, SHAPING, OR EMBOSSING SHEET METAL AND THE Lawrence V. Whistler and Sanford A. Whistler, Kenmore, N. Y.

Application April 7, 1943, Serial No. 482,216

Claims.

Our invention relates to means for forming or drawing sheet metal, and more particularly to a sheet-metal forming structure or assembly with which fluid pressure is employed for drawing or shaping sheet metal and the like to desired form.

In drawing or shaping sheet metal, there is an undetermined pressure required for each drawn stamping or article to be formed, and as now practiced, it has been difficult to draw many articles to desired shape in one operation without the formation of wrinkles, and this is especially true when the metal is drawn unevenly from different marginal portions of a sheet, such as would be required, for example, in articles having a long gradually tapered end wall or walls and a more or less abrupt side wall or walls. Many articles require two or more drawing operations to complete the same; but invariably the finished article will then display draw lines showing the steps between the different draw operations, which are practically impossible to remove.

It is well known that sheet metal varies slightly in thickness at different regions of a sheet and oftentimes a sheet will be found slightly thicker at one end than the other. We have discovered that a definite pressure is required with each new draw-stamping or article, whether rudimentarily formed or formed to finish, and that such pressure must be determined principally by trial, since no ready formula can be applied to all types of draw-stampings and various kinds of material.

It is, therefore, one of the objects of our invention to provide a sheet-metal forming structure or assembly which comprises two parts constructed of heavy steel or other metal hollowed out to form a housing, the two parts of which are to be brought into contact with each other under predetermined high pressure to seal the hollow interior of the housing and render the same fluidtight, or substantially so, one of said parts having a forming-cavity and an abutment or drawface which surrounds the opening or open end of said forming-cavity within said housing and which is surrounded by the fluid-tight contactregions of the two parts of said housing, said abutment or draw-face being adapted to have the marginal portions of a sheet of metal or other similar material which is to be operated upon held thereagainst under pressure, such parts being associated with means for applying pressure to the metal sheet within the area or region surrounded by said abutment or draw-face and with regulatable pressure-transmitting means for restrainedly holding the marginal portions of the sheet against said abutment or draw-face and applying pressure thereto sufficient to prevent wrinkling of the metal while permitting said marginal portions to be drawn inwardly as needed to furnish metal for the drawn portion of the stamping or article being formed.

Another object of our invention is to provide a simple and inexpensive sheet-metal forming structure or assembly wherein pressure can be applied to the marginal portions of a sheet of metal to be operated upon to a degree that will eliminate the wrinkling of the'metal, yet allow the marginal portions of the metal to be drawn inwardly in accordance with the demands of the forming operation while forcing the intermediate portion of the metal into the forming-cavity in said sheet-metal forming structure with a fluid Punch.

A still further object of our invention is to provide such a sheet-metal forming structure or assembly with hold-down means for holding down or restraining movement of the marginal portions of the metal sheet while forming or shaping the same, said means serving to regulate or correct the pressure applied to said sheet by increasing or reducing the same, as found necessary.

With the above and other objects in view to appear hereinafter, our invention consists in providing a sheet-metal forming structure or assembly with a forming-cavity into which a portion of the sheet of metal is to be forced under fluid-pressure and with which is associated a rigid pressure-element adapted to be retained against the sheet of metal to be operated upon around the forming-cavity within said structure or assembly, and to further associate means with said pressure-element for applying pressure thereto or for regulating or correcting the pressures applied thereto.

Our invention further consists in the novel features of construction, in the arrangement and combination of parts, and inthe method of forming sheet metal objects. to be hereinafter described and more particularly pointed out in the subioined claims.

In the drama- Fig. 1 is a longitudinal section through an apparatus or assembly illustrating our invention.

Fi 2 is a horizontal section taken on line 2-2, Fig. 1, looking in the direction of the arrow crossingsaid line.

Fig. 3 is a transverse section taken on line 3-4, Fig. 2, looking in the direction of the arrow crossing said line.

1Fig. 4 is an enlarged section taken on line 4-4,

pressure 01' In the drawings, in which our invention is shown in a representative form, ID designates the lower or pressure-member of the forming or shaping structure or assembly and II the upper or diemember. We prefer to term the lower member III a pressure-member for the reason that fluid under pressure is delivered thereinto from any suitable source and that it also serves to confine a pressure-element, to be hereinafter described, which is to have placed thereagainst a sheet of metal or work-piece which is to be formed to desired shape and which is to be forced against the upper or die-member II with the sheet of metal or work-piece thereon by pressure-transmitting means independent of the fluid-pressure within said pressure-member.

The two members of the assembly are formed of heavy steel or other suitable metal having confronting hollow portions so as to form a housing when in contact with each other. Under the term hollow portion we include any slight depression formed in the upper or die-member in conformity with which the sheet of metal or other workpiece is to be drawn or shaped. Said members may be fastened, respectively, to the bed and ram of a press or die-set so that upon relative movement of said press members, the members of the assembly may be separated to enable a sheet of metal or other material to be placed therein or therebetween, or so that they may be brought into contact with each other under direct pressure exerted by the press.

In the drawings we have shown the forming or shaping structure or assembly as of oblong formation, but it is to be understood that it may be circular or that any other shape may be given the structure or assembly, depending on the par ticular object to be formed therein.

The hollow portion of member In serves as a pressure-chamber or reservoir, designated by the numeral I2, which is surrounded by an upstanding confining wall or walls 3! and in the bottom of this chamber spring-receiving sockets are formed which receive expansion springs 40; the lower ends of which bear against the bottoms of said sockets and the upper ends of which extend upwardly from said sockets into the chamber or reservoir l2.

Supported by said springs is a rigid pressureplate 20 which conforms in outline to the outline of the chamber I 2 but is of somewhat smaller dimensions than said chamber. This pressure plate may be constructed of steel, cast iron, Meehanite, or other suitable material and it normally may have its upper surface in a plane slightly above that in which the upper surface of the lower or pressure-member ID, or more particularly the upper edges or sides of the confining walls 3| thereof are disposed; but regardless of the exact normal position of the pressure-plate, its upward movement is limited by stop-bolts 4|, two of which are shown spaced along each Side of the pressure-plate and two at each end thereof.

The springs 40 bear against the marginal portions of the pressure-plate at opposite sides and ends and they are therefore arranged in an endless series and act to distribute pressure against said pressure plate evenly under certain conditions; the stop-bolts 4| being arranged at intervals between the springs of the endless series. The said stop-bolts are slidable in bolt-holes 42 formed in the bottom wall of the chamber or reservoir l2 and these bolt holes are medially en larged, as at 43, and further enlarged at their lower ends as at 44. The lower end of each of these bolt holes is threaded to receive what we term valve-nuts or valve-plugs 45 provided with conical valve portions 46 at their inner ends adapted to firmly close against valve-seats 41 formed in the bolt holes at the junction of the medial enlargement 43 with the threaded enlargement 44. Since there is a possibility of the pressure fluid leaking along the stop bolts 41 under the pressure applied thereto, the valve-nuts or plugs, when firmly seated against the valve-seats 41, prevent the escape of fiuid along the enlarged lower ends of the bolt holes. The heads 48 of the bolts 4| are adapted to engage the shoulders 49 in said bolt holes to limit the upward movement of the pressure-plate, caused by the action of the several expansion springs 40.

As stated, the pressure-plate 20 is normally raised so that its upper surface is above the plane of the upper surface of the lower or pressure member I0 of the sheet-metal forming assembly, but the parts may be arranged so that the upper surface of said pressure-plate may normally be in line with the upper surface of said lower member, so long as a sheet of metal to be operated upon may be placed thereon and the upper surface of the sheet is slightly above the upper surface of the lower or pressure-member. The material operated upon may determine the normal position of the pressure-plate, and the degree of resistance offered this plate against downward movement is controlled entirely by the combined force of the various expansion springs 40 employed.

A fiuid duct 34 is formed centrally through the pressure plate 20 and a pressure fluid passage 50 is formed in the lower or pressure-member l0. Said passage comprises a duct extending laterally from the center of said member so as to open at the side edge thereof, where it is enlarged, as at 5|, and internally threaded to receive a pipe leading to a source of a fluid pressure medium. The passage 50 terminates in an upward extension 52 which opens into the chamber or reservoir 12 and is in communication through said reservoir with the fluid-duct or opening 34 formed in the rigid pressure-plate.

The upper or die member has a forming-cavity 35 therein which opens outwardly or downwardly to the lower surface of said member and is shaped to the form to which the sheet or metal operated upon is to be fashioned or drawn. Leading from the upper end of said forming-cavity is an air vent 36 which may open to atmospheric air or be led to vent into atmospheric air.

The forming-cavity 35 is considerably smaller in dimensions than the pressure chamber or reservoir 12 so that a considerable area of the under surface of the upper or die member surrounding the open end of the forming-cavity 35 inwardly overhangs the confining or peripheral wall or walls 3| of the pressure chamber or reservoir and serves as a pressure resisting abutment or abutment-surface for the pressure-plate 20, sometimes referred to as a draw-face, said pressureplate being designed to have the sheet of metal to be operated upon placed thereon.

It may here be stated that the upper edge of the confining or peripheral wall or walls 3| of the pressure-chamber or reservoir i2 and the marginal portion of the under surface of the upper or die-member II are polished or dressed so that when brought together, a perfect fit is provided between the two members of the forming or shaping structure or assembly. With a perfect dressing or polishing of these contact portions,

little or no water or other fluid under pressure will escape from between said two members. However, as explained hereinafter, packing may be provided at this region to guard against the escape of the pressure fluid, thus making it impossible to cause a reduction of the pressure within the pressure chamber or reservoir II, or less diflicult to maintain the pressure therein.

Packing interposed between the contact-faces of the two members of the forming or shaping structure or assembly, however, is practical only when the pressure in the pressure-chamber or reservoir I2 is comparatively low, since under high pressure, such as generally used for stamping most types of sheet metal, the packing would be blown out from between the two members. Reliance is, therefore, placed upon the firm contact of the two members around their marginal portions so that under high pressures applied within the pressure-chamber, leakage of fluid between the two members tending to lower the pressure in the pressure-chamber is prevented and a fluid-tight or substantially fluid-tight seam or joint formed by the opposing contacting faces of said members is assured. Under extremely high pressures employed within the pressurechamber or reservoir I2, for certain kinds of work, slight seepage of fluid may occur through this seal or joint and, therefore, where in the claims the term fluid-tight is employed, it is to be considered as including a substantially fluidtight seam or joint, so long as the slight seepage of fluid therethrough does not materially reduce the pressure of the fluid used in said chamber or reservoir as a punch to force the metal sheet or other work-piece into the forming-cavity of the upper or die-member H. The sheet of metal 29 to be drawn to desired shape is placed on the pressure-plate 20 so as to cover the duct or opening 34 and so that its marginal portions are forced by the pressure-plate 20 under the influence of the expansion springs 40 against the abutment surface or draw-face formed by those portions of the lower surface of the upper or die-member which extends inwardly from the side and end walls of said chamber or reservoir l2 and may, therefore, be said to inwardly overhang the said walls. Whatever the normal position of the pressure-plate may be, whether its upper surface is above the upper surface of the lower or pressure-member or substantially in line therewith, the lowering of the upper or die-member against the lower or pressure-member will depress the plate with the metal to be operated upon and cause lowering of the stop-bolts 4|. The series of expansion springs will exert an estimated force against the pressure-plate, which may or may not be exactly that required for effective operation under the principle involved in our invention, since considerable depends upon the nature of the stock operated upon and also upon the gauge, and in some instances the vary ing thickness of the same and the shape to which the stock is to be shaped or drawn. Should the pressure be found excessive so that the stock will not be effectively maintained between the two members of the structure or assembly, but will permit its gradual withdrawal therefrom when the medial portion of the stock is drawn into the forming-cavity of the upper or die-member, there will be a tendency to weaken, fracture, or otherwise damage the metal around the edge of the formity-cavity. It may then be found desirable to remove two or more of the expansion springs so as to reduce the pressure applied to the pressure-plate; the springs being so removed that those retained will apply pressure evenly around the marginal portion of the pressure-plate, or approximately so. If, however, an article is to be formed which varies in depth or if the sheets of metal, or work-pieces as they may be termed, vary in thickness, the pressures applied by the springs to the pressure-plate will be distributed according to the conditions existing and for this purpose certain of the springs may be omitted or additional springs substituted in localized areas of the pressure-plate, or springs less powerful or more powerful substituted for some of those in use. This, therefore, enables the pressures to be applied to localized regions of the pressureplate in exact accordance with the requirements. For best results, generically expressed, the pressure-transmitting means applied to the pressureplate may be termed adjustable, variable, or indedently regulatable, and under the disposition, arrangement, and combination of parts directly associated with these pressure-transmitting means, such means are localized but nevertheless distribute the pressure applied to the pressure-plate over the entire plate, either with like pressures applied to all regions of the plate for transferral to the marginal portions of the sheet of metal or work-piece or with greater pressure applied to one or more regions than to other regions of the plate. This will result in the proper retention of the marginal portion of the stock or work-piece to be operated upon while allowing such portions to gradually creep inwardly under restraint so as to be drawn into the forming-cavity, thus acting upon said marginal portions under sumcient pressure to prevent wrinkling of the marginal portions of the stock and assuring perfectly flat exterior and interior surfaces for the article drawn to shape, even outwardly to the edge of the stock should a rim be retained on the article formed. It will be apparent, therefore, that when in the exemplification of our invention shown, wherein spiral springs are employed as one of many types of pressure-transmitting means, the pressure estimated for the expansion springs 40 is found insufficient, assuming that a complete series of expansion springs is employed, some of the expansion springs may be replaced with others of greater force, or springs of greater force may be substituted for all of the expansion springs. Should it be found desirable to substitute springs of greater force for less than all of the expansion springs employed, the substitute springs will be distributed around the marginal portion of the pressure plate so that the pressure applied to the marginal portion of the stock to be operated upon will be evenly distributed. In any event, should it be found, after forming or stamping one or more pieces of material, that the metal has been weakened by strain, or fractured, or that the metal has developed wrinkles or uneven surfaces during the act of forming the same to desired shape, the pressure may be reduced locally or otherwise, or increased, as may be found necessary. The pressure applied to the pressureplate can, therefore, be easily varied or regulated, either by increasing or diminishing the same, as may be required, and thereafter the stock may be drawn to form within the formingcavity of the assembly with assurance that no weak regions will be created and no wrinkles or uneven regions will be formed in the article.

It will be apparent from the foregoing that, knowing the nature and gauge of the material acted upon and the shape to which the material is to be drawn, experience will enable an operator to closely estimate the pressure which should be applied to the pressure-plate to hold the metal between the same and the abutment surface or draw-face of the upper or die-member with a view of allowing restrained movement of the marginal portions of the metal while forcing the medial portion of the metal into the formingcavity of the metal forming structure or assembly. Properly restrained movement of the marginal or outer regions of the metal, such as provided for with our invention, will prevent wrinkling of the metal and also prevent weakening or fracturing the same. Wrinkling will occur if the marginal or outer regions of a sheet of metal is too loosely held or too firmly retained and in the latter case the excessive pressure would prevent inward movement of the marginal or outer regions of the metal and thus cause a stretching of the metal beyond that which the elongation qualities of the metal would permit, in addition to causing wrinkling of the metal.

It is also apparent that the pressure applied to the pressure-plate can-be varied as required and this can be accomplished with exactitude and speed.

With the assembly constructed and arranged as described, the pressures applied regionally to the pressure-plate, and through the latter to the sheet of metal being operated upon, may be changed as needed so that the metal forced into the forming-cavity from the restrained marginal portions of the sheet can be regulated in accordance with the call or requirements for the same within the forming-cavity during the forming or shaping operation, and also in conformity with the slightly varying thicknesses of the sheet should such exist.

Under the method employed in forming or shaping sheet metal, the pressure per square inch applied to the contacting areas of the two parts of the housing to render the latter fluid-tight may be greater or less than the pressure per square inch applied to the sheet of metal for forming or shaping the same, depending on the area of the forming-cavity wall and in some instances on the metal operated upon, but in all cases the total pressure applied to form the sheet of metal is greater than the total pressure applied to the pressure-plate by its pressure-transmitting means and less than the total pressure used to hold the two parts of the housing together in fluidtight manner.

Having described our invention, what we claim is:

l. A forming assembly for drawing sheet metal to desired form, comprising two members in contact with each other around their outer regions, one of said members serving as a die-member having a forming-cavity into which a sheet of metal to be operated upon is adapted to be forced and an abutment-surface between the outer contact region of said die-member and the formingcavity therein, the other member having a pressure-chamber, the side confining walls of which latter said abutment-surface overhangs, a pressure-plate within said chamber on which the sheet of metal to be operated upon is placed, springs contacting the underside of said pressureplate to force the latter with the sheet of metal thereon against said abutment-surface, said through covered by said sheet of metal, and means to introduce fluid under pressure to said chamber to cause the fluid to initially contact the sheet of metal at the region covering said fluid passage and to contact gradually increasing areas of said sheet as the sheet is forced into said forming-cavity, said springs retaining the marginal portions of said sheet in contact with said abutment-surface while restrainedly releasing said marginal portions under the pressure applied by said pressure-plate during the act of forcing the metal into said forming-cavity.

2. A forming assembly for fashioning sheet metal into any desired form, comprising a diemember having a forming-cavity therein, an abutment region immediately surrounding the open end of said forming-cavity and a contact region surrounding said abutment region, a second member having a chamber with a confining wall whose edge is adapted for contact with said contact region and spring-receiving sockets formed in its bottom wall, a pressure-plate in said chamber having a fluid-duct formed therethrough, spiral springs having their lower ends seated in said sockets and their upper ends engaging said pressure-plate to urge the latter against said abutment region with the marginal portions of a sheet of metal between the two, means to introduce pressure-fluid into said chamber and against said sheet of metal through the fluid-duct in said pressure-plate to force at least portions of the sheet of metal into said forming-cavity, said springs being selected to exert force that will permit the marginal portions of the sheet of metal held against said abutment region to creep inwardly under restraint suflicient to prevent wrinkling of the metal.

3. A forming assembly for drawing sheet metal to desired form, comprising two members marginally in contact with each other, one of said members serving as a die-member having a forming-cavity into which a sheet of metal to be operated upon is adapted to be forced and an abutment-surface between the outer contact region of said die-member and the forming-cavity thereof, the other member having a pressurechamber the side confining walls of which latter said abutment-surface inwardly overhangs, a rigid pressure-plate within said pressure-chamber against which the sheet of metal to be operated upon is placed, pressure-transmitting devices contacting said pressure-plate to force the marginal portions of the sheet of metal placed thereagainst against said abutment-surface, said pressure-transmitting devices being selectively changeable respecting the degree of pressures applied thereby to said pressure-plate, said pressureplate having a fluid opening therethrough spanned by the sheet of metal, and means to introduce fluid under pressure to said pressurechamber to cause the fluid to contact the sheet springs being removable in whole or part and replaceable with springs of greater or lesser force, said pressure-plate having a fluid passage thereof metal and force the same into said formingcavity, said pressure-transmitting devices retaining the marginal portions of said sheet in contact with said abutment-surface while restrainedly releasing said marginal portions under the pressure applied by said pressure-plate during the operation of forcing the sheet of metal into said forming-cavity.

4. A forming assembly for drawing sheet metal to desired form, comprising two members marginally in contact with each other, one of said members serving as a die-member having a forming-cavity into which a sheet of metal to be operated upon is adapted to be forced and an abutment-surface between the outer contact region of said die-member and the forming-cavity thereof, the other member having a pressure chamber the side confining walls of which latter said abutment-surface inwardly overhangs, a rigid pressure-plate Within said pressure-chamber against which thesheet of metal to be operated upon is placed, a plurality of pressure-transmitting devices contacting said pressure-plate at spacedapart regions thereof to force the marginal portions of the sheet of metal placed thereagainst against said abutment-surface, said pressureplate having a fluid opening therethrough spanned'by the sheet of metal, and means to introduce fluid under pressure to said pressurechamber to cause the fluid to contact the sheet of metal and force the same into said formingcavity, said pressure-transmitting devices retaining the marginal portions of said sheet in contact with said abutment-surface while restrainedly releasing said marginal portions under the pressure applied by said pressure-plate during the operation of forcing the sheet of metal into said forming-cavity.

5. A forming assembly for drawing sheet metal to desired form, comprising two members having endless regions in contact with each other in a fluid-tight manner and adapted for movement toward and from each other to permit the insertion of a sheet of metal or other work-piece therebetween, one of said members serving as a die-member having a forming-cavity into which the work-piece to be operated upon is adapted to be forced and an abutment-surface between its contact region and the forming-cavity therein, the other member having a pressure-chamber, the upper edges of the confining walls of which serve as the contact regions for said other memher, said abutment-surface inwardly overhanging said side confining walls, a pressure-plate within said pressure-chamber against which the workpiece to be operated upon is placed, pressuretransmitting means exerting pressure against said pressure-plate to force the marginal portions of the work-piece placed thereagainst said abutment-surface when the two members of the assembly are closed upon each other in fluid-tight manner, said pressure-plate having an opening therethrough covered by said work-piece, and means to introduce fluid under pressure to said pressure-chamber to cause the fluid to initially contact the work-piece and force the latter into said forming-cavity, the pressure transmitted by said pressure-transmitting means being such as to restrainedly release said marginal portions during the act of forcing the metal into said forming-cavity.

6. A forming assembly for drawing sheet metal to desired form under the application or fluid pressure applied thereto, comprising a two-part housing forced together around contact regions thereof under predetermined high pressure to render the same fluid-tight, the parts of said housing being relatively movable to permit of introducing a sheet of metal or other work-piece thereinto, one of said parts having a formingcavity and an abutment-surface surrounding said forming-cavity and surrounded by the contact region of said part, a rigid pressure-element within the other part of said housing against which a work-piece to be formed to shape is placed, pressure-transmitting means exerting pressure against said rigid pressure-element to hold the marginal portions of said work-piece against said abutment-surface, and means to cause fluid to 3 4 ,u muunu be applied to said work-piece in line with said forming-cavity under total pressure less than that the total pressure applied to said contact regions and greater than the total pressure applied against said rigid pressure-element.

7. A forming assembly for drawing sheet metal to desired form, comprising two members formed of rigid material and having contact regions sealpressed tightly against each other to form a fluidtight housing, one of said members having a forming-cavity and a surrounding abutment, both said cavity and abutment surrounded by its sealpressed region, the other member having a fluid pressure-chamber with confining walls which said abutment inwardly overhangs, a rigid pressureplate within said fluid pressure-chamber against which a sheet of metal to be formed is placed, said pressure-plate having an opening therethrough, means to supply fluid under pressure to said fluid pressure-chamber to cause the fluid to pass through said opening and force the sheet of metal into said forming-cavity, and a series of pressure transmitting devices applied to spacedapart regions of said pressure-plate to force the marginal portions of the sheet of metal against said abutment.

8. An apparatus for drawing a sheet of metal to desired form, comprising two co-acting members adapted to marginally contact each other in a substantially fluid-tight manner, one '01 said members having a forming-cavity of varying depths to the conformation of which a sheet of metal is to be formed and an abutment between its contact region and the open end of said forming-cavity, a rigid pressure-element opposed to said abutment against which the sheet of metal is to be placed, said pressure-element having an opening therethrough leading toward said forming-cavity, means to hold the sheet of metal through the medium of said pressure-element against said abutment under localized pressures conforming to the varying depths of said forming-cavity, and means to cause fluid pressure to be applied to said sheet of metal through said opening to force the sheet into said formingcavity and to cause the marginal portions of the sheet to be drawn inwardl in conformity with the requirements for metal at the varying depths of said forming-cavity.

9. An apparatus for drawing sheet metal under fluid pressure, comprising two co-acting elements held together in a fluid-tight manner around regions in contact one with the other and formed to provide a separable chambered-structure having a forming-cavity in one of said elements and an abutment for a work-piece surrounding the open end of said forming-cavity, a rigid pressureplate against one side of which the work piece is to be placed and which is constructed to permit fluid under pressure to contact and force the work-piece into said forming-cavity, a plurality of pressure-transmitting devices transmitting pressure against said pressure-plate to force the marginal portions of said work-piece against said abutment, said pressure-transmitting devices being designed to exert like or varying pressures against said pressure-plate for the purpose of holding the work-piece under desired pressure or pressures against said abutment, and means to deliver fluid under pressure to said work-piece to press the latter into said forming-cavity,

10. In an apparatus for drawing sheet metal under fluid pressure, a fluid-tight housing provided interiorly with a forming-cavity, an abutment surrounding said forming-cavit and 6 aseavva a. chamber toward which said forming-cavity opens, hold-down means wholly within said housing to hold the marginal portions 01 a sheet of metal against said abutment and over said forming-cavity, said hold-down means including a rigid element against which the sheet of metal lies and a plurality of pressure-transmitting devices serving to transmit Pressure to said rigid element at spaced-apart regions thereof and changeable in pressure-transmitting force to 10 Cil vary the degree or Pressure exerted against said rigid element at diflerent regions thereof, and means to direct fluid against the sheet of metal under pressure different from the pressure applied to the marginal contact regions of said members and from the pressures applied by said pressure-transmitting devices.

LAWRENCE V. WHISTLER. SANFORD A. WHISTLER.

Certificate of Correction Patent No. 2,399,775. May 7, 1946.

LAWRENCE V. WHISTLER ET AL.

It isi hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, first column, line 45, claim 5, after the word thereagainstinsert against; and that the said Letters Patent should be read with this correction therein that the-same may conform to the record of the case in the Patent Office.

Signed and sealed this 2d day of July, A. D. 1946.

[smn] LESLIE FRAZER,

First Assistant Commissioner of Patents. 

